1. Field of the Invention
This invention relates to a mainsail furling system containing a boom-mounted furler, intended for use in yachts.
2. Description of the Prior Art
Roller furlers and reefers for use in sail boats are well known, especially in the case of yachts1. These devices provide convenience and ease of use, as they can generally be handled by a single person, usually from the cockpit of the sail boat, and often by the helnsman. This is true even on yachts whose length is in excess of 40 feet, whereas, before the advent of roller furlers is was necessary to have two or more people to handle the hoisting and lowering of sails. However, the convenience of prior art furling systems has often been offset by a diminution in the performance of the sails.
The traditional usage of the word xe2x80x9cyachtxe2x80x9d is used here: a sailing boat used for pleasure. 
Furling and reefing a separate, but related, activities: furling denotes the complete retirement of the sail from use, wherein the furled sail no longer presents any cross section to the wind for the purpose of driving the boat. Reefing, on the other hand, refers to the shortening of sail by reducing the sail area so as to provide less cross section to the wind, reducing the driving force of the wind on the sail. Since most furlers are also used as reefers, the terms will be used interchangeably herein.
Some furlers are designed to be used with sails normally mounted on the stays of a vessel, more particularly on the jibs of sailboats. Others, generally referred to as mainsail furlers, operate on sails which are affixed to two spars at right angles to each other, usually the mast and boom. So-called mainsail furlers are also used on the mizzen sails of ketches or yawls, on the sails mounted on the foremasts of schooners, and so forth. They will all be referred to herein as mainsail furlers for the purpose of this description, and the sails they control will be referred to as mainsails.
Mainsail furlers present a much more difficult design problem than jib furlers, since the jib furler is attached along its luff to a stay, and may be simply wound around the stay like a window shade. The mainsail furler, on the other hand, having two long lines of attachments to two spars perpendicular to each other, has problems unique to its geometry.
Many of the first mainsail furler designs furled the mainsail within the mast (xe2x80x9cmast furlersxe2x80x9d), allowing the foot of the sail to slide along the boom toward the mast when the sail is furled. These system have certain disadvantages over the systems in which the sail is furled on or within the boom (xe2x80x9cboom furlersxe2x80x9d). First of all, the mast furlers require a main part of the apparatus within the mast itself, thereby increasing the weight aloft, and affecting the stability of the vessel under sail. Furthermore, the mast furlers present a nasty maintenance problem, in the case of malfunction or damage to the system. Often, someone is required to go aloft to repair even simple malfunctions, such as jams, which is an unhappy situation for many amateur sailors.
Boom furlers, on the other hand, present their own unique problems. The preferred boom furler at present contains a rotating mandrel mounted within the boom, with a drum at the mast end of the boom. In some embodiments of the prior art the foot rope of the mainsail is affixed to the mandrel along its length. In others, the mainsail is attached only at the tack and clew, that is, the ends of the foot. A winding cord is wound around the drum, and exits through the mast end of the boom. When the sail is hoisted, the winding cord winds itself about the drum; when furled, the user pulls on the winding cord, causing the mandrel to rotate, winding the sail about the mandrel. The drum has large side plates, to keep the winding cord from wandering off the drum and jamming the mechanism. Furthermore, the drum must be rather elongated, since it must fit within the boom, and must provide room for a length of winding cord equivalent to the height of the mainsail, wound about the drum.
A prior art furling system is shown in FIG. 1. Referring now to FIG. 1 (prior art), it is seen that in the luff 2 of the mainsail must be set back at least as far from the mast as the length 1 of the drum in this type of system, plus the width of bearing 4, and distance g of the gooseneck. As a result, the luff 2 is too far removed from the mast 6 to allow a direct connection by sliding a rope sewn into the luff (luff rope) into a slot in the mast, as is commonly done in non-furling mainsail rigging. Instead, a luff extrusion 8 is provided in these prior art systems, to which the luff is attached. Typically, the luff extrusion contains slots to allow insertion of the luff rope, similar to the way the mainsail luff is attached to the mast in non-furler systems. The luff extrusion 8 is affixed to the mast by supports 10, and are affixed non-rotatably to the mast.
Thus, when the boom begins to rotate with respect to the mast, it does so along axis a, which passes through the pin 12 of the gooseneck. The sail, on the other hand rotates about axis b, which, in some prior art implementations, is at some distance from axis a. In such systems, the set of the sail is impaired, and the luff extrusion is subjected to a twisting, with the top of the sail not parallel to the bottom along the luff line. This type of twist diminishes said sail performance.
Furthermore, the large slot is created between the mast and the luff of the sail. Although this so-called xe2x80x9cslot effectxe2x80x9d has been extolled by purveyors of this particular design, it should be noted that no manufacturer to date has introduced this slot in the absence of the need to do so because of the furler design. It is generally believed that such a large slot diminishes sail performance, rather than enhancing it.
Placing the drum at the after end of the boom, and in the current invention, presents a number of improvements over the prior art. Most noticeably, the luff of the sail is in close proximity to the mast, as shown in FIG. 2. The supports have been reduced in size, thereby reducing the torsional stress on the supports caused by the misalignment of the center of rotation of the gooseneck and that of the luff of the mainsail. In some designs, the luff may be attached directly to the mast by means of a mast slot, thus doing away with the supports altogether.
The present design further incorporates a guide which facilitates entry of the lower portion of the mainsail into the opening in the boom through which the mainsail enters. This guide is especially important in the case of the luff end of battens entering the boom opening.
An additional feature of the present invention is the use of a luff-extrusion, which has a U-shaped cross section, with the arms of the U long enough to support the leading edge of the sail battens, and create a compression of the sail batten, thus maintaining the sail shape properly. The reason for this feature may be understood by referring first to FIG. 2a, which shows a prior art system for attaching the mainsail to the mast.
Referring now to this figure, it is seen that the mainsail 110 is attached to the mast 6 by means of a luff rope 112 which slides in a slot in a luff extrusion 8 which is attached to the mast. The boat in this figure is xe2x80x9cin ironsxe2x80x9d, or xe2x80x9cheaved toxe2x80x9dxe2x80x94that is the boat direction 120 is faced directly into the wind 100, and the sail in this figure is accordingly limp, and there are no forces exerted on the luff rope or sail luff. The boat will not advance under this point of sail, but lies motionless in the water, except for the effects of the tide, or the wind blowing on the hull.
When the boat falls off the wind a bit and comes onto close-hauled position, as depicted in FIG. 2b, where the wind 100 is now at an acute angle with respect to the boat direction 120, the situation changes significantly. The sail is attached at its after end, or clew 118, at the after end of the boom. As a result, the pressure of the wind causes the sail to belly out somewhat, as shown, and a compression force vector 114 is exerted on the luff 2 of the sail, driving the luff forward, and out of line with the opening in the luff extrusion 8. The sail invariably contains battens, stiff wood, plastic, or metal material to stiffen the luff.
These battens 122 are located at intervals along the luff of the sail, as shown in FIG. 5, and are set in pockets 124, which maintain the battens in place. They may be any length from a foot or so, to a length which extends along the entire sail, from luff to leech, as is the case depicted in FIG. 5 (xe2x80x9cfully battenedxe2x80x9d sails). The battens are subject to the compressive force caused by the wind during the point of sail shown in FIG. 2b and exacerbate the situation by pushing the battens into the forward end of the batten pockets. The result is to strain the sail material, causing it to chafe or pull apart. In addition, in the case of a fully battened sail, a strain is produced on the junction between the luff 2 and the luffrope 112.
FIG. 2c depicts the situation when the boat falls off still further and the wind 100 is dead aft. The wind still causes the sail 100 to belly, causing compression on the forward end of the sail, as in the previous example. The compression force vector 116, is now almost perpendicular to the direction 120 of the boat, and the chafing strain on the sail, and the compression strain at the junctions between the luff 2 and the luff rope 112 are even more severe than in the situation of FIG. 2b. 
The luff extrusion cross section of the present invention solves the problem of sail wear by preventing the chafing and strain on the junction at the luff rope of the prior art.
On further problem addressed by the current invention involves the strain on the top, or head of the sail, caused by the misalignment of the head and the halyard, a rope which is used to hoist the sail to the top of the mast, and to maintain it there while under sail.
Referring now to FIG. 2d, the prior art is illustrated in regard to the alignment of the main halyard 198 with the center of rotation of the sail about the mast. This drawing illustrates the condition when the wind is blowing aft, and the sail 100 is extended as to be at right angles with the centerline of the boat 134. When the sail 100 is at right angles, as shown in this figure, the length of the halyard between the point where the halyard exits the masthead 130 and the headboard 132 of the sail is distance d2. It is clear from this drawing that when the mainsail 100 is rotated so that it is in line with the centerline of the boat, the distance from the masthead exit 130 and the headboard 132 of the sail will be distance d1. Furthermore, the greater the distance between d3 between the luff 2 and the mast 6, the greater the difference d2xe2x88x92d1 will be. On the other hand, if the axis of rotation of the luff is adjacent to the mast, then d2xe2x88x92d2 will be zero.
In practice, however, d2 is fixed, as the sail is normally hoist to the head of the mast, and cleated down, and this is normally done while the boat is facing directly into the wind. So the distance from the masthead exit to the head of the sail will be d2, and cannot increase without uncleating the halyard. As a result, when the sail attempts to rotate about the mast, the head of the sail will resist this rotation, and the top of the sail will contain a twist, distorting the set of the sail.
The present invention includes a remedy for this prior art problem, in that a mast halyard box is included which prevents twisting of the masthead.
In prior attempts at producing a boom furler with the drum at the after end of the boom, it was found that the extra weight so located made handling of the boom difficult, and placed additional strain on the sail. The present invention addresses this problem by using a solid boom vang to support the boom.
It has been further suggested that the leading of the winding cord through the mast end of the boom, and into the cockpit caused reliability problems with this type of furler. In one embodiment, the use of the winding cord has been eliminated by incorporation of a small, highly geared motor, driving the mandrel directly though a planetary gear system. Thus, the helmsman can operated the furler by means of an electrical switch, located at any convenient place, or places, in the cockpit, and elsewhere. As an alternative embodiment, the motor may be of a type, such as the stepper motor, which may be operated without the use of any gear system.
It is an object of the present invention to provide a sail furling system which is reliable, easy to use, and does not degrade sail performance by its use.
In accordance with one aspect of the invention, the roller furling system includes a hollow boom having a longitudinal axis, an upper surface, a forward end and an after end, with a slot along the upper surface. It includes a mandrel mounted within the boom, having an after end and a forward end, a drum, concentric with the mandrel, and affixed to its after end. Also provided are means to affix a foot of the sail to the mandrel, either along the entire foot, or at the tack and clew only; and means to rotate the drum within the boom. A rotatable boom coupling, affixed at one end to the forward end of the boom, and affixed at the other end to the mast, creates a transverse axis of rotation and also has a vertical axis of rotation parallel to the mast. The boom coupling, being disposed below the boom on the mast, exposes the entire boom slot, so that when the drum is rotated, the sail is furled about the mandrel within the boom.
In accordance with a second aspect of the invention, the furling system also a sail feeder, the sail feeder made up of two side pieces, affixed on either side of the boom slot, and extending upwards along a forward end of the slot, and an end piece, disposed between the boom slot and the mast, attached to each of the side pieces and to the boom itself. The two side pieces and the end piece forms a U-shaped structure when viewed from above, so that the sail is guided into the boom slot by the sail feeder as it exits from the bottom of the luff extrusion as the sail is wound about the mandrel.
In accordance with a third aspect of the invention, the system includes a boom vang, rotatably attached at one end to the base of the mast, and rotatably attached at the other end to an underside of the boom. This arrangement the rotation permits the boom to rotate only about an axis parallel to the mast. The boom vang thus constructed supports part of the weight of the boom, so that the sail shape is not distorted by the weight of the boom.
In accordance with a fourth aspect of the invention, the furling system includes a luff extrusion, having a vertical axis of rotation parallel to and in proximity to the vertical axis of rotation of the boom coupling. This vertical axis of rotation of the luff extrusion is formed by rotatable coupling the luff extrusion to a series of supports, each support rigidly attached to the mast at one end. The luff extrusion have one or more slots extending along its entire length, also have, formed within the extrusion, an extrusion slot, allowing a luff rope of the mainsail to engages with the extrusion slot, so that the mainsail is maintained in a position parallel to the mast and in close proximity to it.
In accordance with a fifth aspect of the invention, the luff extrusion has a vertical axis of rotation at an acute angle to the axis of rotation of the boom coupling. This axis of rotation passes in close proximity to the vertical axis of rotation of the boom coupling at the lowest point of the luff extrusion.
In accordance with a sixth aspect of the invention, the luff extrusion also includes one or more luff extrusion slots extending longitudinally along the length of the luff extrusion. The means to slidingly affix the luff rope to the luff extrusion include means to capture the luff rope within one of the luff extrusion slots.
In accordance with a seventh aspect of the invention, wherein the sailboat has one or more sails which are fully battened, the cross section of the luff extrusion has two or more substantially parallel arms equally spaced to contain the sails and battens. A batten guide is thus formed between each adjacent pair of arms, and the arms of sufficient length to maintain all the battens in compression under sail.
In accordance with an eighth aspect of the invention, the luff extrusion has formed within it the forward end a luff support slot, so that the luff supports are captured within the luff support slot.
In accordance with a ninth aspect of the invention, the system includes a forward bearing affixed to the mast end of the boom, which provides rotational support for the forward end of the mandrel. It includes, in addition, an after bearing, affixed to the after end of the boom, which provides rotational support for the after end of the mandrel.
In accordance with a tenth aspect of the invention, boom also contains a conduit, and the means for rotating the drum include an after pulley, a forward pulley, and a winding line, the winding line winding about the drum, then is redirected by the after pulley through the conduit along the longitudinal axis of the boom, and redirected again by the forward pulley out of the boom. When the sail is raised the drum line is wound about the pulley, the mandrel rotating in one direction, and when the sail is in the raised position and the drum line pulled, the drum and attached mandrel is rotated in the other direction, the sail being wound about the mandrel as a result.
In accordance with an eleventh aspect of the invention, the means for rotating the drum includes a motor, mounted in the after end of the boom in proximity to the drum.
In accordance with a final aspect of the invention, the motor is coupled to the drum by reducing gear means.